Device and method for variable speed lancet

ABSTRACT

A method of penetrating tissue is provided. The method uses a lancet driver to advance a lancet into the tissue; advancing the lancet at a first desired velocity in a first layer of tissue; advancing the lancet at a second desired velocity in a second layer of tissue; and advancing the lancet at a third desired velocity in a third layer of tissue. In one embodiment, the method may including using a processor having logic for controlling velocity of the lancet in each layer of tissue.

RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 10/420,535, filed Apr.21, 2003 now U.S. Pat. No. 7,258,693, which is a continuation in part ofcommonly assigned, U.S. patent application Ser. No. 10/324,053 filedDec. 18, 2002 now U.S. Pat. No. 7,713,214, which is acontinuation-in-part of U.S. patent application Ser. No. 10/127,395,filed on Apr. 19, 2002, now U.S. Pat. No. 7,025,774. Said 10/324,053claims the benefit of priority to U.S. Provisional Patent ApplicationSer. No. 60/374,304 filed Apr. 19, 2002 and copending U.S. patentapplication Ser. No. 10/127,201 filed on Apr. 19, 2002. The presentapplication is also related to U.S. patent application Ser. Nos.10/335,182, 10/335,142, 10/335,215, 10/335,258, 10/335,099, 10/335,219,10/335,052, 10/335,073, 10/335,220, 10/335,252, 10/335,218, 10/335,211,10/335,257, 10/335,217, 10/335,212, 0/335,241, 10/335,183, 10/335,082,10/335,240, 10/335,259, filed Dec. 31, 2002. Said 10/324,053 is alsorelated to PCT Application PCT/US03/12555 filed on Apr. 21, 2003. Allapplications listed above are incorporated herein by reference in theirentirety for all purposes.

BACKGROUND

Lancing devices are known in the medical health-care products industryfor piercing the skin to produce blood for analysis. Typically, a dropof blood for analysis is obtained by launching or driving a lancet intotissue to create a small incision, which generates a small blood dropleton the tissue surface.

Current mechanical lancet launchers are configured to actuateballistically. The lancet is driven out from the opening in the launcherand when a predetermined penetration depth is reached, a return springpropels the lancet back into the housing depth is reached, a returnspring propels the lancet back into the housing with roughly the samevelocity as for the inbound. There is no mechanism to control the lancetin flight (inbound or outbound) other than a hard stop for maximumpenetration. It is therefore impossible to control lancet velocity forskin properties, let alone skin anatomy differences, in these devicesother than a crude depth setting. Known launchers may use steppedoffsets in a range of 0.9 mm to 2.3 mm or switchable end caps to attemptto control lancet depth. The thicker the offset, the shallower theresulting penetration. These depth settings are, in actuality, ameasurement of the protrusion of the lancet tip from the housing, and donot reflect the actual penetration depth of the lancet because oftenting or bending of skin before or during cutting. Unfortunately,without reliable lancet control during actuation, the pain and otherdrawbacks associated with using known mechanical lancet launchersdiscourage patients from following a structured glucose monitoringregime.

SUMMARY OF THE INVENTION

The present invention provides solutions for at least some of thedrawbacks discussed above. Specifically, some embodiments of the presentinvention provide improved control of lancet or penetrating membervelocity. At least some of these and other objectives described hereinwill be met by embodiments of the present invention. In one aspect ofthe present invention, a method of penetrating tissue is provided. Themethod comprises using a lancet driver to advance a lancet into thetissue; advancing the lancet at a first desired velocity in a firstlayer of tissue; advancing the lancet at a second desired velocity in asecond layer of tissue; and advancing the lancet at a third desiredvelocity in a third layer of tissue. In one embodiment, the method mayincluding using a processor having logic for controlling velocity of thelancet in each layer of tissue. In another embodiment, the firstvelocity is at least partially determined based on hydration of thestratum corneum. It should also be understood that the lancet driver maybe electromechanical. The velocity may be determined based on cellpopulation and distribution in the different zones of tissue. Theprocessor may also determine what proportion of electrical powerconsumption is related to the stratum corneum by measuring differencesbetween normal and hydrated stratum corneum. In another embodimentaccording to the present invention, a method is provided for penetratingtissue. The method comprises using a drive force generator to advance apenetrating member along a penetration path into the tissue wherein thepenetrating member having a penetrating member velocity equal to a firstvelocity in a first layer of tissue. Penetrating member velocity isdetermined at a plurality of locations along the penetration path. Themethod also includes adjusting penetrating member velocity at aplurality of locations along the penetration path prior to thepenetrating member coming to a stop in the tissue. In anotherembodiment, the method may further include advancing the penetratingmember at a maximum velocity through the stratum corneum, at a velocityin the epidermis sufficient to reduce shock waves to pain sensor indermis, and at a velocity in the dermis is sufficient for efficientcutting of blood vessels without stimulating pain sensors.

In another aspect of the present invention, a lancing system is providedto drive a lancet during a lancing cycle and for use on a tissue site.The system comprises a lancet driver; a processor coupled to said lancetdriver, the processor configured to adjust lancet velocity to achieve adesired velocity based on the layer of tissue through which the lancetis cutting. The system may include a user interface allowing a user toadjust penetration depth based on stratum corneum hydration. The userinterface may also allow a user to adjust lancet velocity based on userpain. The system may also include memory for storing at least one of thefollowing to determine a skin profile: energy consumed per lancingevent; time of day of. In a still further aspect of the presentinvention, a further method of driving a lancet into a tissue site isprovided. The method comprises calculating stratum corneum thicknessbased on energy consumed and depth of lancet penetration on a previouslancing cycle; driving the lancet into the tissue site, wherein thelancet does not penetrate more than a desired distance beyond thestratum corneum thickness, the stratum corneum thickness determined byan inflection point of energy consumption when the lancet exits thatlayer. A further understanding of the nature and advantages of theinvention will become apparent by reference to the remaining portions ofthe specification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram shows a lancet penetrating layers of the skin in ahistological section.

FIG. 2 is a skin anatomy drawing showing the various skin layers withdistinct cell types.

FIG. 3 shows lancet trajectories plotted in terms of velocity andposition. Line (a) indicates the lancet position, line (b) indicates theskin position as it interacts with the lancet. Line (c) indicates theactual penetration depth of the lancet within the skin.

FIG. 4 is a diagram showing variation of lancet velocity throughdifferent phases of the inbound trajectory.

FIG. 5 shows one embodiment of an invention according to the presentinvention for use with a multiple lancet cartridge.

FIG. 6 is a graph showing a difference in power depending on the levelof stratum corneum hydration.

DESCRIPTION

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed. It should be notedthat, as used in the specification and the appended claims, the singularforms “a”, “an” and “the” include plural referents unless the contextclearly dictates otherwise. Thus, for example, reference to “a material”may include mixtures of materials, reference to “a chamber” may includemultiple chambers, and the like. References cited herein are herebyincorporated by reference in their entirety, except to the extent thatthey conflict with teachings explicitly set forth in this specification.

In this specification and in the claims which follow, reference will bemade to a number of terms which shall be defined to have the followingmeanings:

“Optional” or “optionally” means that the subsequently describedcircumstance may or may not occur, so that the description includesinstances where the circumstance occurs and instances where it does not.For example, if a device optionally contains a feature for analyzing ablood sample, this means that the analysis feature may or may not bepresent, and, thus, the description includes structures wherein a devicepossesses the analysis feature and structures wherein the analysisfeature is not present.

The pain and sufficiency of blood yield of a capillary blood sample fromthe skin may vary based in part on the efficiency of the cutting devicewithin skin layers. Specifically, the ability to control the lancettrajectory in terms of the velocity profile within the spatialconstraints of the skin layers will determine, at least in part, howpainless, and how efficient the cutting is.

There is a regional variation in cell type from the surface of the skindown through the epidermis and dermis. As a nonlimiting example, cuttingthe blood vessels yields blood volumes of about 1-3 μL using lancets ofdiameters 300 to 400 pm at depths of about 0.1-1.5 mm. It is desirable,in one embodiment, to only penetrate deep enough to reach and cut therequired amount of blood vessels for a blood sample. Penetrating toodeep causes more pain than necessary, penetrating too shallow does notyield enough blood or no blood. In one embodiment, cutting thecapillaries in the superficial reticular layer of the dermis with a 300pm diameter lancet is sufficient to yield enough blood to fill currentstate of the art glucose test strips using 0.3-0.5 μL of blood.

In one ideal situation, a painless incision by the lancet would cutenough blood vessels to yield a spontaneous blood sample, which wouldreach the surface of the tissue for analyte testing for such metabolitesas glucose without cutting many nerves or disturbing the elastin fibernet, collagen fibers. Efficient cutting would be defined as controlledlancing for minimal pain to yield a required blood volume for testing ata shallow depth which equates to cutting the capillary mesh in thesuperficial reticular layer.

Using an electronically driven lancet, (where position and velocity areaccurately controlled) the user can fine-tune the cutting processdepending on the cell population and distribution in the differentlayers, for example, based on whether nerves are present or not, orbased on the elastin or collagen fiber content orientation ordistribution.

Accurate depth control relates to generating a spontaneous blood samplewith minimum pain. It is desirable, in one embodiment, to vary thevelocity of the cutting lancet based on the cell population. The surfaceof the skin is comprised of dead or dying cells (the stratum corneum).It is a horny layer, which may vary from 100 μm to 600 μm in thickness,and represents the top layer of the epidermis. The deeper layers of theepidermis can be grouped into 5 different layers, the last of whichseparates it from the dermis. The epidermis has little innervationcompared to the dermis. The distance from the bottom of the stratumcorneum to the capillary loops of the dermal papillae is about 300 μm.In one embodiment, using an electric lancet actuator coupled with aposition transducer, it is possible to resolve position of the lancetwithin the skin to an accuracy of ±17 μm. This translates in to over 40steps through which the velocity can be fed back and controlled. Itshould be understood, of course, that sensors of other accuracies, asknown in the art, may also be used. Embodiments of the invention includedevices and methods to control the velocity of the lancet within thedifferent anatomical layers of the skin to achieve the most efficientcutting. Advantages are achieved by use of a miniaturized electroniclancing system for efficiently cutting through the layers of skin byoptimizing the velocity profile and using position control feedbackmechanism is described.

Referring now to FIG. 1, layers of the skin are shown in thishistological section. Skin is composed of various distinct anatomicalregions (FIG. 1). The main function of the epidermis E is to protect thebody from harmful influences from the environment and against fluidloss. The dermis D is the thick layer of connective tissue to which theepidermis D is attached.

The epidermis E is composed of an outermost layer is the stratumcorneum, which mainly consists of dead keratinized cells. Variations inthe thickness of the epidermis (−0.1 mm. in thin skin, 1 mm or more inthick skin) are mainly the result of variations in the thickness of thestratum corneum (SC). The epidermis E composed of stratum lucidum(consisting of several layers of flattened dead 30 cells), stratumgranulosum (consisting of a few layers of flattened cells) stratumspinosum (cells are irregularly polygonal and often separated by narrow,translucent clefts), and stratum basale. Stratum basale is the deepestlayer or zone of the epidermis and separates the epidermis from thedermis. It consists of a single layer of columnar or cuboidal cells,which rest on the basement membrane. Basal cells are the stem cells ofthe epidermis.

The dermis D is where capillaries and blood vessels are located andnerves supported by connective tissue including collagen fibers andelastin are found. The collagen fibers give the dermis its strength, theelastin and microfibrils give skin its elasticity. Its deepest partcontinues into the subcutaneous tissue without a sharply definedboundary making thickness difficult to determine. It is about 1-2 mm for“average” skin.

For a blood sample to reach the surface of the tissue or skin followinglancing, several factors come in to play. The lancet may cut througheach layer, it may reach the required depth to cut a sufficient numberof blood vessels for the desired blood volume, and then the blood may beable to flow up the wound tract created by the lancet and arrive at thesurface of the skin. If blood arrives at the surface of the fingerwithout “milking” of the finger, this is called a ‘spontaneous’ bloodsample. Generating a spontaneous blood sample is crucial wheninterfacing a measurement unit (e.g. test strip) to the lancing event.The lancet penetration may be deep enough that adequate vessels are cutto release the blood, and not too deep that unnecessary pain isgenerated. Thus accurate depth control is the primary factor controllinga spontaneous blood sample.

Maintaining wound patency is also a factor for achieving a “successful”bleeding event. Many times blood is prevented from flowing upstream thewound channel due to closure of the channel by retraction forces ofsurrounding elastic fibers, which cause the wound channel to closebefore the blood can surface.

Keeping the wound open and allowing spontaneous blood flow can beachieved by slowly retracting the lancet up the wound channel.

As seen in FIG. 1, the thickness of the stratum corneum SC, epidermis Eand dermis D are given for comparison. In one embodiment, the lancet orpenetrating member 10 driven along a penetration path by an electronicdriver 12, may reach the blood vessels located in the dermis D, and cutenough of them to produce a sample of blood for testing. In oneembodiment, the cutting process may be as painless as possible. This maybe achieved by a rapid cutting speed and accurate control of depth ofpenetration.

The ability to control the lancet or penetrating member trajectory interms of the velocity profile of the lancet or penetrating member 10within the spatial constraints of the skin layers may result in lesspainful, more efficient cutting of the skin. In one embodiment, the usercan fine tune the cutting process depending on the skin layer and cellpopulation of the different zones using an electronically driven lancet10, where position and velocity are accurately controlled i.e. whethernerves are present or not as seen in FIG. 2. Specifically, FIG. 2 showsskin anatomy relevant to capillary blood sampling. The skin layers arecomprised of distinct cell types. Variation of lancet velocity based oncell populations in the different layers allows for very precisecutting.

For an electronic or electromechanical lancet driver 12, such as thecontrollable electronic drivers described in copending U.S. patentapplication titled “Tissue Penetration Device” (Attorney Docket No.38187-2551), operating at a lancing velocity in the range of about 4-10m/s is possible. This is two to four times faster than the commonlyavailable mechanically actuated devices, (which operate in the range of1-2 m/s). Ballistic mechanical launcher devices are also not equippedwith position feedback mechanisms. Depth control in these devices isusually by an end cap with stepped offsets. The lancet barrel hittingthe back of the cap controls the lancet depth. The thicker the offset,the shallower the resulting penetration. Users select the depth theyprefer by dialing in the number represented on the device. In oneembodiment, penetration settings vary from about 0.5-2.0 mm with stepsof about 0.2 mm to 0.4 mm. The accuracy of the depth variation is of theorder of ±0.1 mm with the selected puncture depth.

As a nonlimiting example, using an electric lancet driver 12 coupled toan optical position sensor 14, velocity of the lancet 10 may becontrolled at any stage during the actuation and retraction. In oneembodiment, the accuracy of the device in terms of position may bedifferent for the inbound and outbound phase of the movement. Twodifferent types of sensor readings may be applied for the inbound andthe outbound. The current embodiment achieves 70 μm accuracy on theinbound phase using a so called “single (falling) edge detection” and 17μm for the outbound, using a so called “four (rising and falling) edgedetection”. In this nonlimiting example, the accuracy of the velocitycontrol is within 1% at a speed of 5 m/s.

Referring now to FIG. 3 for another nonlimiting example, lancet positionand velocity during an actuation and retraction event is shown. Lancettrajectories in FIG. 3 are plotted in terms of velocity and position.Line (a) indicates the lancet position, line (b) indicates the skinposition as it interacts with the lancet. Line (c) indicates the actualpenetration depth of the lancet within the skin. The difference betweenthe elastic tenting or bending of the skin and the lancet position isthe actual depth of penetration. Skin tenting can account for up to 100μm. Inelastic tenting (the fact that the skin does not return to itoriginal position post lancet removal) is on average about 100 μm. Theinvention focuses on controlling the lancet velocity while on theinbound trajectory in the finger skin.

As seen in FIG. 3, the lancet 10 in one embodiment undergoes anacceleration phase 50 to a specified velocity from where it coasts untilit contacts the skin. This velocity may be preset. At this point anytype of velocity profile can be defined until it reaches the targetdepth. There is a braking period 52 included which allows the lancet 10to come to a complete stop at the selected 20 penetration depth for thisembodiment. The lancet 10 is then retracted from the tissue or finger,and returns to the housing.

Referring now to FIG. 4, the area of interest is the velocity profile100 while the lancet is cutting through the skin layers in the fingeruntil it reaches a predetermined depth. More specifically, variation oflancet velocity through different phases of the inbound trajectory isshown in FIG. 4. In this embodiment, Phase I corresponds to the stratumcorneum, phase II to the epidermis and phase III to the dermis. At eachphase (and during the phase), the options are to maintain currentvelocity, increase current velocity or decrease current velocity. Basedon the thickness of the stratum corneum, velocity could be monitored andchanged in this embodiment at 9 points in the stratum corneum, 6 pointsin the epidermis, and 29 points in the dermis using the four edgedetection algorithm and the 360 strips per inch encoder strip. It shouldbe noted that although the embodiment of the driver discussed hereinproduces the previously discussed number of monitoring points for agiven displacement, other driver and position sensor embodiments may beused that would give higher or lower resolution.

For the purposes of the present discussion for this nonlimiting example,the skin is viewed as having three distinct regions or tissue layers:the stratum corneum SC (Phase I), the epidermis E (Phase II) and thedermis D (Phase III). In one embodiment, the lancet 10 is accelerated toa first desired velocity. This velocity may be predetermined or it maybe calculated by the processor during actuation. The processor is alsoused to control the lancet velocity in tissue. At this velocity, thelancet 10 will impact the skin and initiate cutting through the stratumcorneum. The stratum corneum is hard, hence in this embodiment, maximumvelocity of the lancet 10 may be employed to efficiently cut throughthis layer, and this velocity may be maintained constant until thelancet passes through the layer. Power will likely need to be applied tothe lancet drive 12 while the lancet is cutting through the stratumcorneum in order to maintain the first velocity. Average stratum corneumthickness is about 225 μm. Using a four-edge detection algorithm for theposition sensor 14 of this embodiment, the opportunity to verify andfeed back velocity information can be carried out at 225/17 or roughly13 points. In another embodiment accelerating through the stratumcorneum following impact may improve cutting efficiency. Accelerationmay be possible if the lancet has not reached its target or desiredvelocity before impact. FIG. 4 shows the result of increasing ((a)arrows, maintaining ((b) arrows) or reducing ((c) arrows) velocity onthe lancet trajectory for each of the tissue layers.

On reaching the epidermis E (Phase II), an embodiment of a method maydecrease the velocity ((c) arrows) from the first velocity so thattissue compression is reduced in this second tissue layer. Thus thelancet 10, in this nonlimiting example, may have a second desiredvelocity that is less than the first velocity. The reduced speed in thesecond tissue layer may reduce the pain experienced by the mechanoreceptor nerve cells in the dermal layer (third tissue layer). In theabsence of tissue compression effects on the dermal layer, however,lancet velocity may be kept constant for efficient cutting (i.e. secondvelocity may be maintained the same as the first velocity). In anotherembodiment, velocity may be increased in the second tissue layer fromthe first velocity.

In Phase III, the lancet or penetrating member 10 may reach the bloodvessels and cut them to yield blood. The innervation of this thirdtissue layer and hence pain perception during lancing could be easilyaffected by the velocity profile chosen. In one embodiment, a thirddesired velocity may be chosen. The velocity may be chosen to minimizenerve stimulation while maintaining cutting efficiency. One embodimentwould involve reducing velocity from the second velocity to minimizepain, and may increase it just before the blood vessels to be cut. Thenumber of velocity measurement steps possible for the position sensordescribed above in the dermis is approximately 58. The user woulddetermine the best velocity/cutting profile by usage. The profile withthe least amount of pain on lancing, yielding a successful blood samplewould be programmable into the device.

Currently users optimize depth settings on mechanical launchers bytesting various settings and through usage, settle on a desired settingbased on lancing comfort. Embodiments of the device and methodsdiscussed herein provide a variety of velocity profiles (FIG. 4), whichcan be optimized by the user for controlled lancing, and may include:controlling the cutting speed of a lancet with the lancet within theskin; adjusting the velocity profile of the lancet while the lancet isin the skin based upon the composition of the skin layers; lancingaccording to precise regional velocity profiles based on variation incell type from the surface of the skin down through the epidermis anddermis; lancing at a desired velocity through any tissue layer andvarying the velocity for each layer. This may include maximum velocitythrough the stratum corneum, mediation of velocity through epidermis tominimize shock waves to pain sensors in dermis, and mediation ofvelocity through dermis for efficient cutting of blood vessels withoutstimulating pain receptors.

Referring now to FIG. 5, a processor 120 according to the presentinvention is used to control the lancet driver 122. As previouslydiscussed, a suitable lancet driver may be found in commonly assigned,U.S. patent application titled “Tissue Penetration Device” now U.S. Pat.No. 7,025,774 filed on Apr. 19, 2002. The lancet or penetrating memberdriver may be adapted for use with a cartridge 124 holding a pluralityof lancets or penetrating members 126 which may be actuated to extendoutward as indicated by arrow 128. A suitable cartridge may be found incommonly assigned, copending U.S. patent application Ser. No.10/324,053, now U.S. Pat. No. 7,713,214 filed on Dec. 18, 2002. Thesystem may also include memory 130 for storing at least one of thefollowing to determine a skin profile: energy consumed per lancingevent; stratum corneum hydration; time of day of stratum corneumhydration measurement.

Referring now to FIG. 6, the amount of power used to penetrate into thetissue may increase with increased hydration of the stratum corneum. Thepresent invention provides methods for compensating for variation instratum corneum hydration. Hydration has its strongest effect in theouter layer of the stratum corneum. Studies have shown that coenocytescan swell up to 80% larger on hydration. It is useful to determine whatproportion of electrical power consumption is related the change inthickness of stratum corneum from measuring electrical propertydifferences between normal and hydrated stratum corneum. The presentinvention determines the amount of energy used to achieve a certainpenetration depth at various states of stratum corneum hydration. Byrecording a history of penetration energy and the hydration level, theamount of extra energy used during lancing may be attributed to thechange in thickness of the stratum corneum brought about by increased ordecreased hydration. In one embodiment, the user will adjust penetrationdepth, lancing velocity, lancing velocity for certain tissue layers,time of day, or to account for in stratum corneum variations due tohydration level.

The pain and efficiency of blood yield of a capillary blood sample fromthe skin may very well depend on the efficiency of the cutting devicewithin skin layers. The ability to control the lancet trajectory interms of the velocity profile within the skin layers will determine howpainless, and how efficient the cutting is. Using an electronicallydriven lancet, where position and velocity are accurately controlled theuser can fine-tune the cutting process depending on the cell populationand distribution in the different zones for efficient, painless andreproducible lancing.

While the invention has been described and illustrated with reference tocertain particular embodiments thereof, those skilled in the art willappreciate that various adaptations, changes, modifications,substitutions, deletions, or additions of procedures and protocols maybe made without departing from the spirit and scope of the invention.For example, with any of the above embodiments, the location of thepenetrating member drive device may be varied, relative to thepenetrating members or the cartridge. Some other advantages of thedisclosed embodiments and features of additional embodiments include: ahigh number of penetrating members such as 25, 50, 75, 100, 500, or morepenetrating members may be put on a disk or cartridge; molded body abouta lancet may be used but is not a necessity; manufacturing of multiplepenetrating member devices is simplified through the use of cartridges;handling is possible of bare rods metal wires, without any additionalstructural features, to actuate them into tissue; maintaining extreme(better than 50 micron—lateral—and better than 20 micron vertical)precision in guiding; and storage system for new and used penetratingmembers, with individual cavities/slots is provided. Any of thedependent claims which follow may be combined with any independent claimwhich follows.

Expected variations or differences in the results are contemplated inaccordance with the objects and practices of the present invention. Itis intended, therefore, that the invention be defined by the scope ofthe claims which follow and that such claims be interpreted as broadlyas is reasonable.

1. A lancing system configured to drive a lancet during a lancing cycle and used on a tissue site, the system comprising: a controllable electronic lancet driver coupled to the lancet; a position sensor coupled to the controllable electronic lancet driver, the position sensor configured to detect position and velocity of the lancet in the tissue site; and a processor coupled to said controllable electronic lancet driver, said processor configured to adjust velocity of the lancet to advance the lancet at a first desired velocity in a first layer of tissue, at a second desired velocity in a second layer of tissue, and at a third desired velocity in a third layer of tissue based on feedback of the position and velocity of the lancet from the position sensor.
 2. The system of claim 1 further comprising a user interface on said lancet driver allowing a user to adjust penetration depth based on stratum corneum hydration.
 3. The system of claim 1 further comprising a user interface on said lancet driver allowing a user to adjust lancet velocity based on user pain.
 4. The system of claim 1 further comprising memory for storing at least one of the following to determine a skin profile: energy consumed per lancing event; stratum corneum hydration; time of day of stratum corneum hydration measurement.
 5. The system of claim 1 wherein: said processor has logic for using the lancet driver to advance the lancet into said tissue, said lancet having the lancet velocity equal to the first velocity in the first layer of tissue; adjusting lancet velocity in the skin to achieve the desired velocity based on the layer of tissue through which the lancet is cutting to provide advancement of the lancet at the first desired velocity in the first layer of tissue, at the second desired velocity in the second layer of tissue, and at the third desired velocity in the third layer of tissue. 